1. Field of the Invention
The present invention related generally to dynamometers for tuning motorized vehicles and, more particularly, to devices that utilize rollers that engage the drive wheel of a motorized vehicle to determine engine power and/or produce varying load conditions.
2. Background of the Prior Art
A dynamometer is a commonly used apparatus for determining the engine power of a motorized vehicle including automobiles, trucks and motorcycles. The typical dynamometer operates by braking the rollers that the drive wheel of the vehicle engages and measuring net power of the engine acting on the vehicle drive wheel by sensing the braking power acting on the dynamometer rollers during a time period during which the drive wheel speed is decreased from an initial value to a preset final value.
The optimum measuring capability, accuracy and repeatability of the dynamometer is the direct result of maintained grippage or constant position of the rotating drive wheel in relation to the rotating dynamometer roller through the entire testing period of the engine of the motorized vehicle. Maximizing power transfer between the drive wheel and the roller, is the critical component for optimal performance of the dynamometer. Minimizing the repositioning of the rotating drive wheel relative to the rotating roller (often called xe2x80x9cslippagexe2x80x9d and/or xe2x80x9ccreepagexe2x80x9d) during operation of the dynamometer, maximizes power transfer between the drive wheel and rollers.
Prior art dynamometers attempt to limit slippage and/or creepage between the roller and drive wheel by providing a knurled surface upon the cylindrical surface of the roller. The knurled surface includes a series of alternating longitudinal ridges and grooves positioned parallel to the longitudinal axis of the roller and circumferentially around the perimeter of the roller.
The problem with the knurled surface is that the surface of the drive wheel engaging the roller comes into direct contact with the entirety of the corresponding area of the roller. More specifically, the rubber of the drive wheel not only contacts the ridges but also fills the adjacent grooves of the knurled surface of the roller that the drive wheel engages. This complete contact between the roller and the drive wheel surfaces causes the knurled surface to wear down and the force per unit of surface area of engagement to be minimized. Minimizing the force per unit of surface area of engagement between the roller and drive wheel, increases the slippage and/or creepage between the roller and drive wheel causing reduced power transfer and a corresponding decrease in dynamometer measuring capability, accuracy and repeatability.
A need exists for a dynamometer roller that reduces the surface area of engagement between the roller and drive wheel. Although many variations of dynamometers are available, (see U.S. Pat. Nos. 5,385,042; 5,375,461; 5,036,700; 4,246,779 and 3,516,287), none provide a roller that reduces the surface area of engagement thereby reducing slippage and/or creepage and causing an increase in power transfer between the roller and drive wheel thus optimizing the accuracy and repeatability of the dynamometer.
Another problem with a knurled surface is that the mass and corresponding inertia of the dynamometer roller is substantially the same as a smooth roller surface having the same diameter. Reducing the mass of a dynamometer roller, reduces the dynamometer response time to acceleration and/or power input changes. More specifically, should an internal combustion engine have a cylinder misfire, a reduced mass roller is more likely to respond to the reduced input power provided by the drive wheel.
A need exists for a dynamometer roller having a reduced mass that also includes a reduced surface area of engagement between the roller and the drive wheel. An added dynamometer roller feature that addresses both requirements is to remove material from the surface perimeter of the roller across the entire surface area to a predetermined depth such that the balance of the roller when axially rotated, is substantially unaffected.
It is an object of the present invention to provide a dynamometer having improved accuracy, repeatability, measuring capabilities and reduced mass.
A principal object of the present invention is to provide an improved dynamometer roller design that increases power transfer between the roller and the drive wheel of a vehicle positioned upon a portion of the roller surface. A feature of the improved roller is a reduced area of engagement between the surfaces of the roller and the drive wheel. An advantage of the improved roller is a decrease in the slippage and/or creepage between the engaging surfaces of the roller and drive wheel resulting in improved accuracy, repeatability and measuring capabilities for the dynamometer.
Another object of the present invention is to provide a plurality of spaced, substantially planar surfaces parallel to the longitudinal axis of the improved roller and circumferentially positioned around the perimeter of the roller. A feature of the improved roller is a substantially xe2x80x98flatterxe2x80x99 area of engagement between the surfaces of the roller and drive wheel. An advantage of the improved roller is a substantially uniform force exerted upon the engaging surfaces of the improved roller and drive wheel thereby increasing power transfer between the engaging surfaces.
Yet another object of the present invention is to provide a plurality of spaced recesses substantially parallel to the longitudinal axis of the improved roller and circumferentially positioned around the perimeter of the roller. A feature of the improved roller is a reduced area of engagement between the spaced surfaces and the vehicle drive wheel. An advantage of the improved roller is an increase in the number of roller edges engaging the drive wheel, and a corresponding increase in the power transfer between the planar surfaces of the roller and the drive wheel.
Still another object of the present invention is to optimize the relationship between the lateral dimensions of the planar surfaces and the recesses in the dynamometer roller surface. A feature of the improved roller is the lateral dimension of the planar surfaces being triple the lateral dimension of the recesses. An advantage of the improved roller is the increased force per unit area of engagement between the planar surfaces and the drive wheel, and increasing the power transfer between the roller and the drive wheel which improves dynamometer performance.
Another object of the present invention is to reduce the mass and corresponding inertia of the dynamometer. A feature of the improved roller is the removal of material from the roller""s perimeter across the cylindrical surface of the roller to a predetermined depth. An advantage of the improved roller is increased sensitivity and reduced response time to acceleration and/or power input changes from the drive wheel of a vehicle engaging the cylindrical surface of the improved roller.
Briefly, the invention provides an improved dynamometer roller engaging the drive wheel of a vehicle, the improvement comprising a plurality of spaced recesses circumferentially positioned in an outer wall of the roller, said recesses forming a plurality of spaced, substantially planar surfaces circumferentially positioned around the perimeter of the roller, said planar surfaces ultimately engaging the drive wheel of the vehicle thereby limiting slippage and/or creepage between the drive wheel and the roller resulting in increased power transfer between the drive wheel and roller, and increased dynamometer accuracy and repeatability.